Constant pressure syringe for surgical use

ABSTRACT

A closed system for harvesting fat through liposuction, concentrating the aspirate so obtained, and then re-injecting the concentrated fat into a patient comprises as its main components a low pressure cannula having between about 7 to 12 side holes of about 1-2 mm by 2.0 to 4.0 mm, a spring loaded syringe holder with a constant force or coiled ribbon spring to apply a substantially constant pressure over the full excursion of the plunger, and a preferably flexible collection bag which is also preferably graduated, cylindrical over most of its body and funnel shaped at its bottom, all of which are connected through flexible tubings to a multi-port valve. The multi-port valve has two flutter/duck bill valves which restrict the fluid flow to a one way direction which effectively allows the syringe to be used to pump fat out of a patient and into a collection bag in a continuous manner. After the bags are centrifuged to concentrate the fat, the excess fluids are separated and the valve is re-connected to permit the syringe pump to reverse fluid flow to graft the concentrated fat back into the patient.

CROSS REFERENCE TO RELATED APPLICATION

Priority is claimed to provisional U.S. Patent Application Ser. No.60/828,505 filed Oct. 6, 2006 entitled Method and Apparatus forLipotransfer, the disclosure of which is incorporated herein byreference.

BACKGROUND AND SUMMARY OF THE INVENTION

The autologous grafting of liposuctioned tissue holds much promise inplastic surgery; but being very technique dependent, and lacking asimple apparatus to perform it, it has a reputation for beingimpractical and unreliable. Generally, as presently performed in theprior art, the process requires harvesting with suction cannulasdelicate and finicky adipocytes, separating them, concentrating them,and then re-grafting them a droplet at a time into a three-dimensionalrecipient matrix in aliquots small enough to survive through diffusionyet separated enough to avoid crowding. The process becomes extremelyarduous and time consuming when large volumes are involved. One of theinventors herein has previously invented methods and apparatus forperforming fat grafting as shown in pending U.S. patent application Ser.No. 11/409,294, filed Apr. 21, 2006 and entitled Method and System forPreparing Soft Tissue for Grafting, Enhancing Grafting Results, andGrafting Autologous Fat to Soft Tissue Such as the Breast, thedisclosure of which is incorporated herein by reference. This processand method represents a significant breakthrough and improvement overthe prior are but leaves room for further improvement and refinement.The inventors herein have invented a system comprised of a number ofdevices each of which is novel but which also function together in anovel way to streamline, simplify and implement fat grafting with apractical procedure having a more predictable success.

The process of liposuction, or the harvest of subcutaneous fat, iscommonly performed with a lipoaspirator machine that generates about oneatmosphere vacuum pressure and has a collection flask connected inseries between the suction cannula and the vacuum pump. It is wellaccepted that one atmosphere vacuum pressure is most effective if theintent is to simply remove and discard the fat to reduce excesses inbody contour. However, if the intent is to reinject this aspiratedtissue as a graft, one atmosphere pressure is too high as it inflictssignificant damage to the adipocytes sufficient to render themundesirable for reinjection. Therefore, for the purpose of re-graftingor reinjection it is generally known that lower vacuum pressures, closerto one half an atmosphere should be used to yield better fat graftsurvival. If lower pressures are used however, it reduces the efficiencyof liposuction.

The grafting of lipoaspirated fat is increasingly being recognized as amethod of restoring volume defects and of improving body contourabnormalities such as may be found in the cheeks, the breast or thebuttocks. In addition, tissue carefully harvested by liposuction hasbeen shown to be rich in stem cells capable of regenerating tissue andof improving a number of conditions related to scarring, radiationdamage and even aging. Therefore a method and device that would makethis process of low pressure harvesting, processing and re-injectinglipoaspirated fat simple, practical and reliable would be of greatutility.

The inventors have succeeded in developing such a system that utilizes anumber of novel components uniquely suited to low pressure harvesting oflipoaspirated fat. Each of these components themselves have novel andinventive aspects to them, and together comprise a closed system that isuniquely suited to harvesting fat for reinjection.

The inventors closed system includes as its components a very lowpressure, multiple opening, cannula for aspirating the fat from thepatient; a constant, controlled low pressure syringe mechanism forcontrollably liposuctioning the aspirate out of the patient with minimaldamage to the adipocytes; and a collection bag into which the aspirateis deposited. A multi-port routing valve interconnects these threecomponents with several ports of the routing valve having internal duckbill valves for one way routing of the aspirate both as it is collectedand as it is re-injected. Although reference is made throughout thisdisclosure to a duck bill or flutter valve, it should be understood thatthose terms apply to any design that opens completely and widely, withminimal pressure gradient, which avoids the slit-like openings of othervalve constructions, for example, that force the fat cell suspension tobe damaged as it accelerates through the narrow opening. To performeither of the aspiration or re-injection, the syringe mechanism isrepeatedly operated to in effect “pump” the fluid through the multi-portrouting valve with its one way internal valves. In this way, theaspirate is collected without being exposed to the atmosphere and at lowpressures so as to minimize the damage to the delicate and sensitiveadipocytes. After collection, the bag is disconnected from the routingvalve and one or more bags may be centrifuged at low pressures, such aswith a manual centrifuge, to separate the aspirate within each bag intoits components of serum, concentrated fat and free oil. After beingcentrifuged, the supernatant oil is purged from the top of the bag, theserum fluid is purged from the bottom port, and the concentrated fatremains in the bag for re-injection. To perform re-injection, the bagand cannula are connected to the routing valve at each other's ports asused for aspiration. This connection one-way routes the concentrated fatout of bag into the patient by means of the duck bill valve orientation.Then, after the routing valve and cannula are primed, the very lowpressure syringe is repeatedly operated to withdraw the concentrated fatfrom the bag, and then push it through the routing valve and into thepatient. Alternatively, instead of the spring syringe system, a small1-5 ml syringe is preferably used with a simple spring on the plungerwhich brings it automatically back each time the surgeon's fingers pushdown on it to empty the grafts into the patient. Throughout this processthe aspirate is not exposed to the air, only very low pressures are usedto move the aspirate through the system, a low speed centrifuge is usedto concentrate the fat from the aspirate which can be collected intomultiple bags to speed the concentration process, and the same systemcomponents used to collect the aspirate are used to re-inject theconcentrated fat. This closed system and method provide significantimprovements over the prior art, and will more fully understood byreferring to the drawing figures and description of the preferredembodiment that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a multi-hole cannula suited for very lowpressure harvesting of lipoaspirate;

FIG. 2(a) is a perspective view of a spring activated syringe aspirator;

FIG. 2(b) is an exploded view of the aspirator of FIG. 2(a);

FIG. 2(c) is an exploded view of an alternate design aspirator with twosmaller helicoidal springs;

FIG. 3 is an assembled but transparent view of the syringe aspirator,with a syringe installed therein;

FIG. 4 is a side view of the routing valve, with cutaway detailing thevarious flow paths of aspirate therethrough;

FIG. 5 is a schematic side view detailing the re-arrangement of therouting valve for re-injection of the fat into a patient;

FIG. 6 is a side view of the routing valve detailing its arrangement ofone way valves within it for multi-use such that the same routing valvemay be used for both aspiration and re-injection, depending upon whichof the open side ports is occluded and which is connected to thesyringe;

FIG. 7 is a side view of a lipo-grafting bag partially filled withaspirate separated into its components such as by centrifuging;

FIG. 8 is a perspective of a manual centrifuge particularly useful inon-the-fly centrifuging during a surgical procedure; and

FIG. 9 is a perspective view of the assembled system, having thecannula, routing valve, activated syringe aspirator and lipo-graftingbag all connected in a closed system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As has become known in the art, grafted fat globules have to firstsurvive by diffusion and what is called plasmatic imbibition until theyget revascularized from the recipient bed. Larger globules that have alower surface to volume ratio cannot get enough nutrients to survive andtherefore die off before getting revascularized. This improvedunderstanding of the physiology of graft survival led to the use ofsmaller bore cannulas with smaller openings that harvest smallerglobules of fat. While generally speaking the smaller the better, verysmall is impractical in terms of harvesting efficiency, especially whenlarge volumes are required for the particular procedure. It is wellrecognized today that the ideal harvesting cannulas should havediameters between 2-3 mm and harvesting slits (hole openings) between0.5 and 3 mm.

The most commonly used and commercially available cannulas forliposuction are either blunt ended with a single side hole, three sideholes (Mercedes type) or have an open end protected by a buckethandle-like shield (the Coleman harvesting cannula). While there arealso some cannulas with up to six side holes, they are less popular, andto the inventors' knowledge, never scientifically proven to be superiorto the more commonly used ones. Furthermore, with the standard pressuresused for liposuction, it is commonly believed based on use that too manyholes clog up the preferred small bore cannulas otherwise thought to beuseful for this application.

The inventors are unaware of work in the prior art evidencing thatprogressively increasing the numbers of side holes, while maintainingthe optimal catheter bore of 2.4-2.7 mm and the slit opening of about1.0-2.0 mm by 2.0-4.0 mm can not only improve the efficiency of fatharvesting (volume harvested per to-and-fro stroke of the cannula) butalso achieve excellent harvesting yield at vacuum pressures much lowerthan previously described.

In a study conducted by the inventors, a series of cannulas withincreasing number of side holes (Coleman design, one, two, three and upto nine side holes) were connected to a liposuction aspirator machinethat was progressively dialed down to the gentlest vacuum that wouldstill yield a continuous flow of fat. In three patients the inventorsmeasured at each pressure and with each cannula, the volume oflipoaspirate per 10 strokes in comparable fresh tumesced fields. Theresults confirmed that yield of fat per pass increased linearly with thenumber of side holes in the cannula. Cannulas with 9 holes proved mostefficient at harvesting with pressures as low as 240 mm/Hg. Cannuladiameter was best at 2.4 mm for the skinny patients and 2.7 mm for themore fibrous & obese. This, to the inventors' knowledge, establishes forthe first time that liposuction can be effectively performed withexcellent yield at very low pressures (250-350 mmHg or ⅓ atmospheric)that cause minimal damage to the tissue provided a cannula was used with9-12 side slit like holes measuring about 1.0-2.0 mm by 2.0-4.0 mmdepending upon the bore diameter. With increased bore size, larger holesit is thought could be effectively used to achieve similar results.

As shown in FIG. 1, a cannula 20 comprises a body 22 with a tip 24 whichis inserted within a patient to harvest fat. The body has three seriesof holes 26, each series comprising three holes 26 aligned along thebody length. The other side of the body 22 (not shown) is left intact. Acentral bore 28 may also be provided, as desired.

The inventors postulate that increasing the number of side holes beyond9 and even up to 12 might further improve the process, and have foundsuch results with 12 hole cannulas. However adding too many holes canbecome problematic for two reasons: (a)—structural: more side holesweaken the cannula and there is a real danger that the cannula couldbreak while inside the patient requiring an incision and a scar toretrieve it (a complication that occurred when a poorly designed 12 sidehole cannula was tried; and which would be avoided by the inventorsarrangement of side holes not spread over the entire cross sectionalcircumference of the cannula but instead be limited to about half thecircumference, leaving the other half circumference intact to maintainstructural integrity); (b)—impractical: having too many side holes alongthe shaft of the cannula restricts the excursion range of theliposuction motion as the more proximal holes cause loss of vacuum whenthe cannula is retracted close to the skin insertion site during theback and forth excursions required for liposuction.

The cannula length depends upon the requirements of the patient and theanatomical area to be harvested and the preference of the surgeon. Wemade cannulas for various uses that vary between 15 to 45 cm in length.To avoid breaks and maintain structural integrity the side holes arepreferably aligned along half the circumference, keeping the remaininghalf structurally intact.

Liposuction with the intent to re-inject the harvested tissue iscommonly performed using a syringe and manual pressure generation. Theproblem with this approach is not only cramping and fatigue of theoperator's hand but also inability to effectively control the level ofvacuum achieved. (The hand can generate very high vacuum pressures thatwill destroy a lot of the fat cells, and especially after fatigue andlack of control, the hand often pulls ineffectively with suboptimalpressures). Thus the need for a mechanically activated device that, onceactivated, would pull on the syringe plunger with a constant forcethroughout virtually its entire stroke from completely collapsed inwardto full extension.

While the most simple mechanical design is a spring connected to theplunger, the problem is that commonly available coil springs do not havea flat stress strain curve, especially over the long range of excursionof the syringe plunger that are required for liposuction. We thereforeinvented an apparatus that pulls the plunger of a syringe over itsentire excursion range with the same constant force to generate aconstant controlled low atraumatic negative pressure of about 250-350mmHg. This syringe holder 30 is shown in FIGS. 2 and 3. This apparatusincludes either a set of springs judiciously designed and arranged toprovide a constant force over the entire long range of excursion, or,preferably a specially designed spring construction that uncurls with aconstant force, as shown as item 32 in FIG. 3.

The subject of the invention herein is preferably a device that canactivate a syringe to pull a relatively constant controlled negativepressure over the entire range of its excursion. The inventors haveconceived a number of designs whereby mechanical energy can be storedand then induced to deliver a constant pull force over substantially theentire range of excursion of the plunger. This includes hydraulic or gaspressure activated devices that are either self contained with thehydraulic energy stored within the device or devices that are connectedto a source of hydraulic energy whether a gas tank or a separate pump. Agas tank of the kind generally available in the operating roomsconnected to a pressure regulator device a hose and a mechanicaltransducer to activate the syringe plunger is also a alternative meansof generating a constant vacuum pressure. Alternatively, a batteryoperated electric pump can also be the source of energy that can drivethe syringe plunger with a constant force to generate a constantnegative pressure over its entire range of excursion.

For a purely mechanical (no hydraulic and no electrical) design, thereare a number of alternative means of connecting the syringe plunger tothe spring, including direct connection or indirect with cables andpulleys. The device can be designed to accept standard disposablesyringes and once cocked, can pull on syringe plunger to generate thedesired constant vacuum. Alternatively, instead of the device being anactivator for standard disposable syringes, the device can incorporateits own pistons and cylinders as a stand-alone device that does not needto be loaded with extraneous syringes.

As shown in greater detail in FIGS. 2 and 3, the syringe holder may bemade from molded parts, such as a bottom receiver 34 and cover 36 (shownassembled in FIG. 2(a)). A pair of rings 38 extending from a bracket 40provide a connection point for one or more springs (not shown). Thecustom made syringe device shown in FIG. 3 includes the syringe butt 42encased in a handle 44. A spring casing 46 provides storage for thehelicoidal spring 32, which is preferably used as has been found by theinventors to provide a relatively constant pressure over the course ofits winding and unwinding.

Even if the vacuum pressure of the lipoaspirator machine is dialed downto atraumatic low levels, harvesting the fat with a vacuum source inseries with the collection reservoir has been found by the inventors tobe untenable for many reasons: 1—The collection bottle has to be rigidlest it collapses with the vacuum defeating its function as a reservoir;2—The collection bottle has to remain vertical, lest the harvested fatcontinues its way with the aspirated air flow towards the vacuum pump.This is impractical as it forces the collection reservoir to remain on adedicated stable fixed stand away from the mobile surgical field; 3—thisrequirement adds a few additional feet of tubing with significantopportunity for dead space losses to form; and most importantly,4—adipocytes are well known to be damaged by dessication from highvolume air flow and from air splashes in the collection bottle uponevery instance of vacuum loss (and these tend to be quite frequentwhenever one of the liposuction cannula holes gets close to the skinentrance site).

As an improvement over this prior art, the inventors have developed afat harvesting apparatus whereby the vacuum source and the collectionreservoir are not in series but are rather isolated from each other in aparallel type of configuration. To that effect, the inventors designed arouting valve that isolates the collection reservoir from the vacuumsource and depending upon the applied pressure gradient directs the flowof fat aspirate either towards the vacuum source syringe or towards thecollection bags used for separation and re-injection. Compared to manualliposuction whereby each time a syringe is filled, it has to bedisconnected from the cannula and replaced with an empty one, not onlyis the requirement for syringe supplies reduced but more importantly theoperating time has been found to be reduced by half.

While there are in the market a number of prior art valve based devicesintended to direct the flow of an aspirate or an injectate from areservoir to the recipient source or, acting in reverse from a source toa reservoir, these devices proved not suitable for this applicationwhere the fat is intended to be re-injected. The pressure gradientrequired to reverse flow from opening to closure of the valve ispreferably as close to zero as possible. Hence, all the spring-baseddesigns are not suitable. Furthermore, the flow across the valve has tobe as unrestricted as possible to prevent the damaging highvelocity/high shear flow that a slit like opening from the membranebased valve designs would necessarily impose. Similarly, the rotaryvalves and other ball valves tend to crush the adipocytes as they close.

The inventors have found that the duckbill and the flutter type ofvalves are preferred for this application, for the following reasons.They require very little pressure gradient to open, they open over theentire bore of the tubing, they close gently without snapping to causeminimal damage to the adipocytes, they have no added moving parts, andcan be molded out of biocompatible rubber like material.

Thus, the inventors developed a routing valve consisting of two duckbillor flutter valves positioned in the arrangement presented in FIG. 4 forharvesting and a reversed arrangement shown in FIG. 5 for re-injecting.However, a design modification described in FIG. 6 allows the same valvesetup device to be used for both purposes provided a different fourthopening is plugged or connected to the syringe.

More particularly, as shown in FIG. 4, a three port multi-valve 50 has afirst port 52 for connection with, for example, a Luer lock 54 to asyringe 56, a second port 58 for connection with another Luer lock 60 toa cannula (not shown), and a third port 62 with a Luer lock (64) forconnection to tubing (not shown) for carrying the aspirated fat to acollection bag (not shown). Each of ports 58 and 62 have an associatedpreferably rubber flutter/duck bill valve 66, 68 respectively whichallow one way flow through their associated ports. Preferably, a hardinner sleeve 70 in each valve 66, 68 prevents eversion of theflutter/duck bill valve. As shown in FIG. 5, the valve 50 may beconstructed with the flutter/duck bill valves oriented differently toallow for fat grafting or re-injection. As shown in FIG. 6, a four portmulti-valve 72 may be provided to allow for either aspirating orgrafting, merely be re-connecting the components to different ports.With the set up described above, free oil supernatant accumulationvolume (a measure of adipocyte damage) and percentage graft take were atleast as good as historical controls performed with a manual syringe.With the four port valve as shown in FIG. 6, in harvesting/aspirationmode, the cannula is connected to port D, the syringe to port B, thecollection bag to port C and port A is plugged off. Ininjection/grafting mode, The cannula is connected to port C, the syringeto port A, the collection bag to port D and port B is plugged off.

The tissue aspirated with the cannula, using the syringe driver, isrouted by the valves through sterile tubing to cylindrical candle likecollapsible bags 80 as shown in FIG. 7 with multiple ports at both endsand a bucket handle type or loop 82 at the top. The bag 80 consecutivelyfunctions as: 1—a collection reservoir; 2—a low speed centrifuge tube;3—a concentration device that allows purging out of the separated serumat the bottom, the free oil and accumulated air at the top throughseparate vents/ports 84, 86 respectively; 4—a re-injection bag with aport 88 at the bottom connected through tubing 90 to the muting valve inre-injection mode, and graduations that provide reading of the volume ofconcentrated fat grafted.

It is generally accepted that high speed centrifugation destroys thefragile adipocytes and while many surgeons still prefer 3000 rpm @ 1-2minutes centrifugation, there is evidence that even this separation stepwill lead to loss of valuable components from the aspirated tissue suchas stem cells, platelets, and fluid rich in growth factors. Therefore,especially for large volume lipografting many authorities now prefersimple gravity decantation to separate the components of the suctionedfluid. The problem with gravity separation is that it is typically veryslow, and especially should the patient be undergoing surgery. Toaccelerate this process, while avoiding the limitation of a regularcentrifuge, the inventors designed a rotating table top hanger 92 asshown in FIG. 8 for the bags 80. The rotation is done manually and thespeed is around to 100-200 rpm.

All the above individual inventions are organized to work together inharmony. Together, they comprise a closed harvesting, collection,separation, concentration and re-injection system that inflicts minimaldamage to the adipocytes, minimal exposure to air, minimal manipulationof the aspirated material, minimal exchange of syringes and cannulas. Inaddition, it is practical in that it saves time, effort and supplies,which is especially important to achieve better results with less riskof harm to the patient.

Shown together as a complete closed system in FIG. 9, liposuction isperformed with the cannula 100, using the constant pressure device 102,the fat cells are routed by the valves 104 to the collection bag 106where excess aspirated air is vented. The bags 106 are centrifuged bycentrifuge 92 shown in FIG. 8. After centrifugation, the supernatant oilis purged from the upper port and the serum fluid from the bottom portof the bags. The cannula and the constant pressure device arereconnected to the proper ports of the valve, and the bag connected to adifferent port. The concentrated fat is then re-injected through thetubing connecting the bag to the valve working in injection mode.

The inventors describe a novel device that is especially practical forlarge volume adipocyte harvesting and grafting. It is believed that thisinvention reduces operative time and labor while maintaining excellentgraft viability and take. By harvesting at a low constant pressure andkeeping a closed system with minimal exposure to air, minimal transferof the aspirate and manipulation of the fat, the inventors havestreamlined the harvesting, concentrating and grafting steps and madethe procedure practical and reproducible using reduced amounts ofsupplies, effort, and time.

While the inventors have disclosed their invention in the form of theirpreferred embodiments, this disclosure should be understood as merelyillustrative and not limiting in any sense. Various changes andmodifications would be apparent to those of ordinary skill in the artupon reading and learning from the inventors teachings contained herein.Those changes and modifications are fully intended to fall within thescope of the invention which should be limited only by the scope of theclaims appended hereto.

What is claimed is:
 1. A syringe driver device, comprising: a housingfor engaging a body of a syringe, wherein the housing extends along anaxis that is parallel to the body of the syringe when the syringe isengaged with the housing, and wherein the housing includes an opening ina side of the housing extending along the axis of the housing; a bracketfor engaging a plunger of the syringe, wherein the bracket extendsthrough the opening in the housing transverse to the axis of thehousing; and a spring attached to the bracket, the spring being biasedto move the bracket and thereby withdraw the plunger from the body ofthe syringe at a constant force.
 2. The syringe device of claim 1wherein the spring comprises a constant force spring.
 3. The syringedevice of claim 2 wherein the constant force spring comprises a coiledribbon spring.
 4. The syringe device of claim 2 further comprising acasing for housing the constant force spring.
 5. The syringe device ofclaim 4 wherein the constant force spring comprises a coiled ribbonspring.
 6. The syringe device of claim 5 wherein the opening guidesmovement of the bracket as the bracket moves in an aspirating direction.7. The syringe device of claim 1 further comprising a casing for housingthe spring.
 8. A device comprising: a syringe having a proximal end anda distal end; a plunger slidably received within a body of the syringeand having a first end and a second end, wherein the second end of theplunger extends beyond the distal end of the syringe body; a housingengaging an outer surface of the syringe body, wherein the housingincludes a first opening and a second opening positioned onsubstantially opposite sides of the syringe body; a bracket engaging thesecond end of the plunger beyond the distal end of the syringe body,wherein the bracket extends transverse to the syringe body and extendsthrough the first opening and the second opening; wherein the bracket ismoveable between a first position in which the first end of the plungeris adjacent to a proximal end region of the syringe and a secondposition in which the first end of the plunger is adjacent to a distalend region of the syringe; and a spring connected to the bracket andextending to a distal region of the housing, wherein the spring isconfigured to move the bracket from the first position to the secondposition at a constant force.
 9. The device of claim 8, wherein thehousing is releasably engaged to the outer surface of the syringe bodyand the bracket is releasably engaged to the plunger.
 10. The device ofclaim 8, wherein the spring includes a coiled ribbon spring.
 11. Thedevice of claim 8, wherein moving the bracket from the first position tothe second position aspirates the syringe.
 12. The device of claim 8,wherein the housing engages a distal end of the syringe body.
 13. Thedevice of claim 8, wherein the syringe is removably mounted in thehousing.
 14. The device of claim 8, wherein the spring applies asubstantially constant force to the bracket as the bracket moves theplunger from the first position to the second position to aspirate thesyringe.
 15. The device of claim 8, wherein movement of the bracket fromthe first position to the second position defines a stroke length of thebracket and a stroke length of the plunger, and wherein the springapplies a substantially constant force on the bracket along the entirestroke length of the bracket to cause a substantially constantaspirating pressure within the syringe as the plunger moves along thestroke length of the plunger.
 16. A device comprising: a housing locatedat a proximal region of the device, wherein the housing is dimensionedto receive a distal portion of a syringe, and wherein the housingextends along an axis that runs parallel to the syringe when engagedwith the housing, and wherein the housing includes a slot formed in aside of the housing; a bracket slidably connected to the housing,wherein the bracket extends transverse to the axis of the housing andincludes a gripping portion that extends through the slot; a springoperably coupled to the bracket and extending from the bracket to adistal region of the device; and a casing located at the distal regionof the device, wherein the casing contains at least a portion of thespring, wherein the bracket is slidable between a proximal region and adistal region of the housing, and the spring is configured to apply asubstantially constant force on the bracket to slide the bracket fromthe proximal region to the distal region of the housing.
 17. The deviceof claim 16, wherein the spring includes a coiled ribbon spring.
 18. Thedevice of claim 16, wherein the gripping portion includes a ring. 19.The device of claim 16, wherein the gripping portion includes a curvedsurface.
 20. The device of claim 16, wherein the housing is formed of afirst piece and a second piece that are configured to cooperativelyengage the syringe.
 21. A syringe driver device, comprising: a syringe;a housing engaging a body of the syringe, wherein the housing includes afirst longitudinal slot extending along the housing and positioned on afirst side of the syringe, and wherein the housing includes a secondlongitudinal slot extending along the housing and positioned on a secondside of the syringe, opposite the first side; a bracket engaging aplunger of the syringe, wherein the bracket extends transversely throughthe first longitudinal slot and the second longitudinal slot; and aspring attached to the bracket, the spring being biased to move thebracket and thereby withdraw the plunger from the body of the syringe ata constant force.
 22. A device comprising: a syringe having a proximalend and a distal end; a plunger slidably received within a body of thesyringe and having a first end and a second end, wherein the second endof the plunger extends beyond the distal end of the syringe body; ahousing engaging an outer surface of the syringe body, wherein thehousing includes a longitudinal slot extending along an axis of thehousing substantially parallel to an axis of the syringe, wherein theslot forms an opening through a side of the housing; a bracket thatextends along an axis transverse to the axis of the housing and the axisof the syringe, wherein the bracket engages the second end of theplunger beyond the distal end of the syringe body, wherein the bracketextends transversely through the longitudinal slot; wherein the bracketis moveable between a first position in which the first end of theplunger is adjacent to a proximal end region of the syringe and a secondposition in which the first end of the plunger is adjacent to a distalend region of the syringe; and a spring connected to the bracket andextending to a distal region of the housing, wherein the spring isconfigured to move the bracket from the first position to the secondposition at a constant force.
 23. A device comprising: a syringe; ahousing located at a proximal region of the device, wherein the housingreceives a distal portion of the syringe and extends substantiallyparallel to a longitudinal axis of the syringe; a first longitudinalslot extending along a first side of the housing; a second longitudinalslot extending along a second side of the housing such that the syringeis positioned between the first longitudinal slot and the secondlongitudinal slot; a bracket engaging a plunger of the syringe andslidably connected to the housing along an axis transverse to thelongitudinal axis of the syringe, wherein the bracket includes agripping portion that extends transversely through the firstlongitudinal slot and the second longitudinal slot and projects out fromthe first longitudinal slot and the second longitudinal slot; a springoperably coupled to the bracket and extending from the bracket to adistal region of the device; and a casing located at the distal regionof the device, wherein the casing contains at least a portion of thespring, wherein the bracket is slidable within the first longitudinalslot and the second longitudinal slot between a proximal region and adistal region of the housing, and the spring is configured to apply asubstantially constant force on the bracket to slide the bracket fromthe proximal region to the distal region of the housing.